Continuous Production of Tailored Silver Nanoparticles by Polyol Synthesis and Reaction Yield Measured by X-ray Absorption Spectroscopy: Toward a Growth Mechanism
Two complementary topics are discussed: (i) the continuous production of silver nanoparticles (AgNPs) and (ii) the measurement of reaction yield by X-ray absorption near-edge spectroscopy (XANES). The continuous polyol synthesis of AgNPs in grams amount and in the size range of 7-104 nm was carried out in the segmented flow tubular reactor (SFTR). Particle size was tailored by controlling the synthesis parameters such as temperature, reactant concentrations, and polyvinylpyrrolidone (PVP) molecular weight. The continuous production was tested for 4 h, and the product has shown constant particle size distribution over the whole production time. Reliable continuous production of 2.3 g h(-1) of similar to 100 nm AgNPs can be achieved with a lab-scale SFTR. The produced particles were fully characterized with respect to size, size distribution, and chemical purity. To better understand the growth mechanism, synchrotron-radiation high-resolution X-ray diffraction, and X-ray absorption spectroscopy data were collected directly on the AgNPs suspension. In particular, from}CANES experiments, the conversion yield of Ag+ to Ag-0 was measured. The results are consistent with a two-step process where PVP controls the particle nucleation while growth is ensured by thermally induced ethylene glycol oxidation.